Broach



June 13, 1961 J. A. PSENKA 2,987,801

BROACH Filed 00 s, 1958 2 Sheets-Sheet 1 FIG.2.

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INVENTOR. JOSEPH A. PSENKA gZzZ ATTORNEYS June 13, 1961 .1 A. PSENKA 2,987,301

BROACH Filed Oct. 6, 1958 O 2 Sheets-Sheet 2 FIGS.

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IN V EN TOR.

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United States Patent 2,987,801 BROACH Joseph A. Psenlra, Bloomfield Hills, Mich., assignor to National Broach & Machinery Company, Detroit, Mich, a corporation of Michigan Filed Oct. 6, 1958, Ser. No. 765,478 6 Claims. (Cl. 29-951) The present invention relates to a broach and more particularly, to a broach comprising a plurality of sections a leading one of which is a roughing section adapted to rough out the teeth of an internal gear or splined element, and a following section which is a finishing section adapted to finish the teeth of the work piece with extreme accuracy.

It is an object of the present invnetion to provide a broach of the character described in which the finishing section is connected to the leading roughing section with some provision for relative movement so that the finishing section will locate itself accurately in the work piece and will therefore produce teeth on the work piece which for practical purposes have the same accuracy as the teeth on the finishing section of the broach.

More specifically, it is an object of the present invention to provide a two section broach comprising a leading roughing section and a following finishing section connected together so that the following finishing section may float relative to the leading section.

Still more specifically, it is an object of the present invention to provide a two section broach as described in the foregoing in which the following finishing section is connected to the leading section for relative axial and circumferential movement with respect to the leading section.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention, wherein:

FIGURE 1 is a side elevational view of the leading roughing section of the breach.

FIGURE 2 is an end view of the leading section of the broach seen from the right in FIGURE 1.

FIGURE 3 is a side elevational view of the broach assembly.

FIGURE 4 is an enlarged fragmentary sectional view through the trailing end of the broach assembly.

FIGURE 5 is an end view of the finishing section alone as seen from the right in FIGURE 4.

FIGURE 6 is a longitudinal sectional view of the nut used in the assembly.

FIGURE 7 is an end view of the nut as seen from the left in FIGURE 6.

FIGURE 8 is a diagram showing the traces of roughing and finishing teeth.

In the breaching of internally toothed members such as internal gears, spline members or the like, it is possible to produce broaching elements having substantially any required degree of accuracy. However, in use, such a broaching element can reproduce itself with substantially perfect accuracy only when it is not subjected to stresses and strains occasioned by an earlier stage of a breaching operation. In order to permit a broaching member to perform substantially perfect reproduction of its own accuracy, the present invention contemplates a broach assembly comprising a roughing section adapted to initiate and substantially complete the formation of the internal teeth. Connected to the roughing section of the broach assembly for limited movement relative thereto is an extremely accurate finishing section. The finishing section is connected to the roughing section for relative movement, preferably both axially and circumferentially, so that it may accommodate itself to the roughed out teeth in the work piece and finish these teeth with extreme accuracy.

Referring now to the drawings, the leading section of the broach assembly is seen in FIGURES l and 2 at 10 and comprise a head 12 adapted to be connected to a suitable device for pulling the broach through a hole in a work piece. Conveniently, the roughing section of the broach as indicated generally at 14 in FIGURE 1, includes a series of continuous annular blades or ribs '16 adapted to machine the hole in the work piece to true cylindrical formation. Following the continuous annular blades 16 there are provided a series of progressively stepped blades 18, the blades 18 being interrupted as best seen in FIGURE 210 form separate cutting teeth 20. It will be appreciated that the cutting teeth 20 are arranged in axial alignment if the broach is for the purpose of producing spur teeth, or in helical alignment if the broach is for the purpose of producing helical teeth. The term longitudinal alignment or the like is intended to cover arrangements for both spur and helical gears. At the following end of the leading section 10 of the broach assembly is a cylindrical support 22 having a reduced portion 24 which forms a shoulder 26 for a purpose which will subsequently appear. Rearwardly of the reduced section 24 the support portion 22 is threaded as indicated at 28.

Directly in rear of the final toothed blade 30 of the roughing section there is a cylindrical surface 32 opposite sides of which are machined away as indicated to form rearwardly facing flat abutment surfaces 34 and radially outwardly facing flat surfaces 36. This arrangement provides a fiat transversely extending key 38 for a purpose which will presently appear.

As seen in FIGURE 3, the following finishing broach section or shell 40 is assembled on the support portion 22 of the leading section 10 and is retained thereon in assembled relation by a nut 42 threaded to the threaded portion 28 of the roughing or leading broach section.

The detailed construction of the finishing section 40 is best seen in the sectional enlargement of FIGURE 4 and the end view of the finishing section seen in FIGURE 5. The finishing section is essentially tubular in shape having toothed cutting blades 44 forming longitudinally aligned series of cutting teeth 46. Again, the cutting teeth extend in axially disposed series if the broach is to form a spur member, and the series are helically aligned if the broach is used to produce helical teeth on the work piece. At its leading end, which is the left hand end as seen in FIGURE 4, the finishing section 40 is provided with a notch or keyway 48 extending diametrically across the leading end thereof and dimensioned to receive the key 38 at the following end of the roughing section 10 of the broach. The finishing section 4.0 is provided with a central opening 50 the intermediate portion of which is enlarged to provide clearance and the ends of which are of slightly reduced size to provide the guide surfaces 52 and 54 which are guidingly received on the cylindrical surface of the support portion 22 of the roughing section of the broach.

It will be observed that the nut 42 in assembly has its forward end engageable with the annular shoulder 26 previously described. Forwardly of its threaded portion 56 the nut is slightly enlarged as indicated at 58 and the enlarged cylindrical opening therein snugly receives the reduced portion 24 of the roughing section of the broach. Similarly, at its rear end the nut 42 is provided with a cylindrical surface 60 adapted to snugly engage the reduced end portion 62 of the roughing section of the broach. At its rear end the nut 42 has a cylindrical por- Patentecl June 13, 1961 The keyway at the leading one of the finishing section of the broach has a dimension of nous .0000

Thus, taking the dimensions representing maximum permissible error, it will be observed that the width of the keyway is .002 wider than the width of the key received therein. This .002 clearance, While not large, is neverless suificient to permit limited circumferential relative movement between the roughing md finishing broach sections. It will of course be appreciated that the key and keyway on the roughing and finishing sections are properly related with respect to the cutting teeth thereon so that the cutting teeth on the finishing section are in substantially true alignment with the teeth on the roughing section. Nevertheless, as the finishing section moves into action, it is permitted to float so that it aligns itself with substantially perfect accuracy with respect to the teeth as partially roughed out by the roughing section of the broach.

In addition to the circumferential movement permitted, it will be observed in FIGURE 4 that the leading end 68 of the nut is slightly spaced from the trailing end of the finishing section 40 of the broach. In this figure the clearance is exaggerated for clarity. In practice, a clearance which may be between .0005 and .0015 is provided. This clearance is not so much for the purpose of providing for axial movement of the trailing finishing broach section 40 on the leading roughing broach section as it is to insure that the trailing section 40 is not clamped against substantially free circumferential movement relative to the leading section of the broach.

Preferably, the first annular series of teeth on the finishing section, seen at 72 in FIGURE 4, is tapered at the frontend to form a pilot section.

The pilot section follows the last series of teeth on the roughing section closely enough to insure continuous guiding action.

The teeth of the remaining series of teeth on the finishing section are given side clearance, as for example about which may vary somewhat for helical gears.

Another feature which contributes to accuracy in the finished gear is the provision of a slot '75 at the bottom of each tooth space out by the roughing section. The teeth of the finishing section are of less height than those of the roughing section and hence cut only on the sides.

Thus, the surface 77 of FIGURE 8 may represent the.

outline cut by the last tooth of the roughing section, and

surfaces 78 and 79 represent surfaces cut by succeeding teeth of the finishing section. The top portions of the teeth of the finishing section are thus able to pass in clearance through the grooves or slots 75.

'The spectacular improvement in accuracy which is produced by the present broach can perhaps best be appreciated by recognizing some of the diificulties inherent external guide means. This however, leads to inaccuracim due to -inaccuracies between the lead bar and breach,

torsion in the lead bar and manufacturing inaccuracies inherent in producing a long one-piece broach. These inaccuracies are reflected in inaccuracies in the finished piece. When employing a short shell as a finishing section, problems of lead, spacing, size and form are minimized. Furthermore, reproduction of involute or other form from the short shell section to thepiece is always obtained.

' Secondly, it is possible to machine both spur and helical teeth in a work piece by an operation in which the broach or work is permitted to float, and in which the broach or work picks up its rotation as the teeth are partially broached into the material of the gear. This operation in general consists of an initial cutting phase in which the teeth are not formed to extend at the proper lead, and in addition are somewhat mutilated. Thereafter, as the broach is drawn through the work piece and the tooth spaces are cut to greater depth, more accuracy in the guiding of the broach is developed, and with a sufliciently long broach rather accurate teeth are formed. However, at best the operation is a compromise and accuracy in the following section of the broach is precluded by inaccuracies resulting from engagement between the leading portion of the broach and the work piece.

In the present case the following finishing section of the broach floats ,so that it aligns itself with the partial tooth spaces formed by the roughing section. Its function is primarily to remove a small amount of metal and finish'the teeth of the work piece to final exact dimensions. The roughing operation will have produced teeth which are approximately accurate and the finishing section will be guided through the substantially completely cut tooth spaces with great accuracy and will for all practical purposes reproduce its own accuracy in the teeth formed in the work piece.

It is desirable to prevent looseningofnut 42, when broaching a helical gear, to provide the threads of a hand opposite to that of the gear.

The drawings and the foregoing specification constitute a description of the improved broach in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

l. A broachassembly for breaching internally toothed members comprising a generally cylindrical leading broach section having series of longitudinally aligned progressively stepped roughing teeth and provided at its following end with arearwardly extending cylindrical support portion which has a-reduced portion forming an annular shoulder, a generally tubular finishing broach section of a lesser length than the distance between said leading broach section and the said reducedportion having .an opening centrally therethrough piloted in accurately guided relation upon said cylindrical support. portion, means loosely interconnecting said leadingsection and said finishing section to limit circumferential movement of said finishing section on the support portion of said leading section, a nut threaded to the rear end of the support portionof said leading section, said nut having an enlarged cylindrical opening engaging said reduced portion and abutting said shoulder thereby preventing clamping engagement of said finishing section between said nut and the portion of the leading section of said broachhaying roughing teeth.

2. A broach assembly comprising a leading roughing section having sen'es of longitudinally aligned progressively stepped cutting teeth, a flat key and supp'ort section integrally formed on said roughing section at the rear ofthe'last series of cutting teeth, said support section having a guiding surface, a following finishing section having longitudinally aligned series of progressively stepped cutting teeth in longitudinal alignment with the series of teeth in said leading section, said cutting teeth of said finishing section having side clearance in back of the cutting edges, a longitudinal bore in said finishing section, and a transversely extending keyway extending diametrically across the leading end of said bore, said bore receiving said guiding surface and said keyway loosely receiving said key, and means retaining said finishing section on said support section to permit limited circumferential movement between the sections.

3. A broach assembly comprising a leading roughing section having series of longitudinally aligned progressively stepped cutting teeth for cutting tooth spaces terminating at the bottom in wide grooves, a fiat key and support section integrally formed on said roughing section at the rear of the last series of cutting teeth, said support section having a guiding surface, a following finishing section having longitudinally aligned series of progressively stepped cutting teeth in longitudinal alignment with the series of teeth in said leading section, said teeth of said finishing section being of less height than the final series of teeth on said roughing section whereby the teeth of said finishing section pass in top clearance through the grooves being cut when said assembly is in operation, a longitudinal bore in said finishing section, and a transversely extending keyway extending diametrically across the leading end of said bore, said bore receiving said guiding surface and said keyway loosely receiving said key, and means retaining said finishing section on said support section to permit limited circumferential movement between the sections.

4. A broach assembly for broaching internally toothed members comprising a generally cylindrical leading broach section having series of longitudinally aligned progressively stepped roughing teeth and provided at its following end with a rearwardly extending cylindrical support portion which has a reduced portion forming an annular shoulder, a generally tubular finishing broach section of lesser length than the distance between the last tooth of said series and said shoulder of said reduced portion, having an opening centrally therethrough piloted in accurately guided relation upon said cylindrical support portion, means interconnecting said leading section and said finishing section to limit circumferential movement of said finishing section on the support portion of said finishing section, said means including a transversely extending keyway provided at the leading end of said following finishing section, and a fiat transversely extending key integrally formed on said shaft portion and loosely engaging said transversely extending keyway, said key and keyway connection permitting limited circumferential movement between the leading roughing section and the following finishing section, a nut threaded to the rear end of the support portion of said leading section, said nut having an enlarged cylindrical opening engaging said reduced portion and abutting said shoulder thereby preventing clamping engagement of said finishing section between said nut and the portion of the leading section of said broach having roughing teeth.

5. A broach assembly for broaching internal gears comprising a main elongated body having at its leading end a generally cylindrical rough breaching section provided with series of longitudinally aligned progressively stepped roughing teeth and provided at its following end with a reduced cylindrical portion forming an accurate supporting and guiding surface and a rearwardly facing shoulder at the leading end of said reduced cylindrical portion, said shoulder having a transversely extending key thereon, a threaded extension at the rear end of said reduced cylindrical portion, a tubular finishing shell having series of longitudinally aligned progressively circumferentially stepped side cutting finishing teeth, said shell having an accurately finished cylindrical bore supporting and guiding said shell on said reduced cylindrical portion, said shell having a keyway having a transverse dimension slightly greater than that of said key in which said key is loosely received to provide for limited circumferential movement of said shell on said reduced cylindrical portion, a threaded abutment member on said threaded extension, locating abutment surfaces on said threaded abutment member and said body to located said threaded abutment member in operating position, a forwardly facing shell abutment surface on said threaded member, the distance between said shoulder and the shell abutment surface on said threaded member when said threaded member is located by engagement between said locating abutment surfaces being slightly greater than the length of said shell to prevent clamping of said shell on said body and so to provide for limited circumferential movement of said shell on said body.

6. A broach assembly for breaching internal gears comprising a main elongated body having at its leading end a generally cylindrical rough breaching section provided with series of longitudinally aligned progressively stepped roughing teeth and provided at its following end with a reduced cylindrical portion forming an accurate supporting and guiding surface and a rearwardly facing shoulder at the leading end of said reduced cylindrical portion, a removable abutment member at the following end of said reduced cylindrical portion having a forwardly facing shell abutment surface, locating means acting between said body and abutment member to locate said shell abutment surface a predetermined distance from said rearwardly facing shoulder, a generally tubular finishing shell having series of longitudinally aligned progressively circumferentially stepped side cutting finishing teeth, said shell having an accurately finished cylindrical bore supporting and guiding said shell on said reduced cylindrical portion, said shell having oppositely facing abutment surfaces engageable with said shoulder and said abutment member, said abutment surfaces being spaced apart a distance slightly less than the distance between said shoulder and the shell abutment surface of said abutment member, and key means comprising a key and keyway provided between said body and shell, said key being slightly narrower than said keyway to provide for limited circumferential movement of said shell on said body.

References Cited in the file of this patent UNITED STATES PATENTS 1,197,132 Lapointe Sept. 5, 1916 1,806,552 Atwood May 19, 1931 1,935,774 Halborg Nov. 21, 1933 1,969,977 Halborg Aug. 14, 1934 FOREIGN PATENTS 22,248 France Dec. 21, 1920 414,331 Great Britain Aug. 2, 1934 592,888 Great Britain Oct. 2, 1947 

